Method Of Marking Hydrocarbon Liquids

ABSTRACT

The invention concerns a method of marking a hydrocarbon liquid comprising the 
     
       
         
         
             
             
         
       
     
     step of adding to said liquid, as a tracer compound, a compound of Formula I or Formula II:
     wherein at least one of R 1 -R 6  in Formula I and at least one of R 7 -R 14  in Formula II is selected from:
       i. a bromine or fluorine atom;   ii. a partially or fully halogenated alkyl group;   iii. a branched or cyclic C 4 -C 20  alkyl group;   iv. an aliphatic substituent linking two positions selected from R 1 -R 6  in Formula I to one another or two positions selected from R 7 -R 14  in Formula II to one another; or   v. a phenyl group substituted with a halogen atom, an aliphatic group or halogenated aliphatic group
 
and none of R 1 -R 6  in Formula I and none of R 7 -R 14  in Formula II being a sulphonate group or COOR 15 , where R 15  represents H, C 1 -C 20  alkyl, C 2 -C 20  alkenyl, C 2 -C 20  alkynyl, C 3 -C 15  cycloalkyl or aryl.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.15/590,145 filed May 9, 2017 (now allowed), which is a continuation ofU.S. patent application Ser. No. 14/116,668 filed Dec. 11, 2013, nowU.S. Pat. No. 9,678,054 issued Jun. 13, 2017, which is National Stage ofInternational Patent Application No. PCT/GB2012/051015 filed May 9,2012, which claims priority to U.K. Application No. 1107870.6 filed May11, 2011, the disclosures of each of which are incorporated herein byreference in their entireties for any and all purposes.

The present invention concerns marking hydrocarbon liquids with tracermaterials for identification purposes, in particular hydrocarbons whichare taxable or liable to be subject to tampering or substitution such asgasoline and diesel fuels for example.

It is well known to add tracers to hydrocarbon liquids. A typicalapplication is the tagging of hydrocarbon fuels in order to identify theliquid at a subsequent point in the supply chain. This may be done foroperational reasons, e.g. to assist in distinguishing one grade of fuelfrom another, or for other reasons, in particular to ensure fuelquality, deter and detect adulteration and to provide a means to checkthat the correct tax has been paid. Apart from fuels, other products,such as vegetable oils may be marked to identify the product produced ata particular source, or certified to a particular standard.

One problem which is known to exist with the marking of fuel liquids inparticular, is the potential for the tracer to be removed, byevaporation from the fuel, by degradation of the tracer through aging orexposure to environmental conditions such as heat, sunlight or air oralternatively by deliberate removal of the tracer for unlawful purposessuch as for avoidance of tax. Methods for deliberate removal of tracersinclude adsorption of the tracer onto common adsorbent materials such ascharcoal or clays, exposure to radiation, such as ultraviolet light,oxidation etc. A useful fuel tracer therefore needs to be resistant toremoval by these common methods and also to more sophisticatedtreatments such as treatment with acids and/or bases. It is an object ofthe invention to provide a method of marking hydrocarbon liquids whichis more resistant to removal of the tracer than known methods.

WO2011/032857 describes hydrocarbon markers based on aromatic compoundsin which at least two of the substituents are carboxyl groups, i.e.COOR, where R represents H, C₁-C₂₀ alkyl, C₂-C₂₀ alkenyl, C₂-C₂₀alkynyl, C₃-C₁₅ cycloalkyl or aryl. We have found that aromaticcompounds having carboxyl substituents may be less resistant to removalfrom hydrocarbons than the compounds used as tracers in the method ofthe present invention.

According to the invention, a compound of Formula I or Formula II is

used as a tracer compound for the marking and identification ofhydrocarbon liquids:

-   wherein at least one of R¹-R⁶ in Formula I and at least one of    R⁷-R¹⁴ in Formula II is selected from:    -   i. a bromine or fluorine atom;    -   ii. a partially or fully halogenated alkyl group;    -   iii. a branched or cyclic C₄-C₂₀ alkyl group;    -   iv. an aliphatic substituent linking two positions selected from        R¹-R⁶ in Formula I to one another or two positions selected from        R⁷-R¹⁴ in Formula II to one another; or    -   v. a phenyl group substituted with a halogen atom, an aliphatic        group or halogenated aliphatic group        and further wherein none of R¹-R⁶ in Formula I and none of        R⁷-R¹⁴ in Formula II represent a sulphonate group or COOR¹⁵,        where R¹⁵ represents H, C₁-C₂₀ alkyl, C₂-C₂₀ alkenyl, C₂-C₂₀        alkynyl, C₃-C₁₅ cycloalkyl or aryl.

We also provide, according to the invention, a method of marking ahydrocarbon liquid comprising the step of adding a compound of Formula Ior Formula II as a tracer compound to said liquid and subsequentlyanalyzing a sample of a hydrocarbon liquid for the presence of saidtracer compound to determine whether said sample is a sample of saidmarked hydrocarbon liquid.

We also provide, according to the invention, a hydrocarbon liquidcontaining a tracer compound at a concentration of less than or equal to500 ppbv, wherein said tracer compound is a compound of Formula I orFormula II:

and wherein at least one of R¹-R⁶ in Formula I and at least one ofR⁷-R¹⁴ in Formula II is selected from:

-   -   i. a bromine or fluorine atom;    -   ii. a partially or fully halogenated alkyl group;    -   iii. a branched or cyclic C₄-C₂₀ alkyl group;    -   iv. an aliphatic substituent linking two positions selected from        R¹-R⁶ in Formula I to one another or two positions selected from        R⁷-R¹⁴ in Formula II to one another; or    -   v. a phenyl group substituted with a halogen atom, an aliphatic        group or halogenated aliphatic group        and further wherein none of R¹-R⁶ in Formula I and none of        R⁷-R¹⁴ in Formula II represent a sulphonate group or COOR¹⁵,        where R¹⁵ represents H, C₁-C₂₀ alkyl, C₂-C₂₀ alkenyl, C₂-C₂₀        alkynyl, C₃-C₁₅ cycloalkyl or aryl.

The hydrocarbon liquid may be a pure compound such as hexane or octaneor it may comprise a mixture of compounds such as a distillationfraction having a particular range of boiling points. The hydrocarbonliquid may be intended for use as a chemical, a solvent or a fuel. Theinvention is of particular use for marking liquid hydrocarbon fuels suchas gasoline and diesel fuels. Therefore, in a preferred embodiment ofthe use and method of the invention, the hydrocarbon liquid comprises adiesel fuel, a gasoline fuel or a solvent. In one particular applicationof the method, a low-tax fuel such as an agricultural diesel may bemarked in order to detect any subsequent sale and use for purposes suchas road-vehicle fuel which would normally be taxed more highly. In suchcases unlawful dilution or substitution of a more highly taxed fuel withthe low-taxed fuel may be detected by analysis of the highly taxed fuelto determine whether the tracer is present. Therefore in these cases, itis highly beneficial to use a tracer compound in the low-taxed fuelwhich is not easily removed, or laundered, from the fuel to a level atwhich it can no longer be detected. We have found that compounds ofFormula I and Formula II are resistant to removal from hydrocarbon fuelsby several known methods of fuel laundering.

Preferably, when any of R¹-R¹⁴ is a halogen or halogenated alkyl group,the halogen atom is selected from bromine or fluorine and thehalogenated alkyl group is a bromoalkyl or fluoroalkyl group. Thehalogenated alkyl group(s) may be partially or fully halogenated, linearor branched, acyclic or cyclic aliphatic groups. Preferred halogenatedalkyl groups include trifluoromethyl, 1,1-difluoroethyl, fluoroallyl,heptafluoropropyl, tridecafluorohexyl, heptadecafluorooctyl. Mostpreferably at least two R substituents in either Formula I or II consistof a halogen atom or a halogenated alkyl group.

Alkyl group substituents may be straight chain or branched acyclic orcyclic aliphatic groups, preferably consisting of 4-12 carbon atoms.Branched or cyclic aliphatic groups are preferred. Preferred groupsinclude tert-butyl, 1,1-dimethylpropyl, 2,2-dimethylpropyl (neo-pentyl),1,1-dimethylbutyl, 1-ethyl-1-methylpropyl, 2,2-dimethylbutyl,1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl,1-ethyl-2,2-dimethylpropyl, 1-methylethyl-2,2-dimethylpropyl,1,1,3,3-tetramethylbutyl, cyclopentyl, cyclohexyl, 2-methylcyclohexyl,3-methylcyclohexyl, 4-methylcyclohexyl, 2-ethylhexyl, 1-adamantyl,2-adamantyl and decahydronaphthyl groups. Particularly preferred aresubstituents including quaternary substituted carbon atoms, such astertiary butyl. In one preferred embodiment, at least one of R¹-R¹⁴ inFormula I or Formula II comprises an aliphatic or halogenated alkylsubstituent containing a quaternary-substituted carbon atom.

It is preferred that none of R¹-R⁶ in Formula I and R⁷-R¹⁴ in Formula IIinclude fused aromatic rings such as naphthyl or anthracenyl, saturatedheterocycles where the heteroatom is anything other than oxygen,unsaturated heterocycles, amino, imino, N-oxide, nitro, hydroxyl,carboxyl, ester, amide, acetal, thiol, thiol ethers, disulfides,sulfoxide, sulfone, sulfonate, phosphite ester, phosphate ester,cationic, anionic or zwitterionic groups; or metal containingsubstituents. It is possible, however, to use a molecule containing oneof the above unpreferred groups provided that sufficient halogen,halogenated alkyl or bulky alkyl groups of the preferred type arepresent in the molecule to provide resistance to laundering. Preferablythose R¹-R⁶ in Formula I and R⁷-R¹⁴ in Formula II which are not selectedfrom a bromine or fluorine atom; a partially or fully halogenated alkylgroup; a branched or cyclic C₄-C₂₀ alkyl group; an aliphatic substituentlinking two positions selected from R¹-R⁶ in Formula I to one another ortwo positions selected from R⁷-R¹⁴ in Formula II to one another; or aphenyl group substituted with a halogen atom, an aliphatic group orhalogenated aliphatic group are H.

Suitable tracer compounds include 2,3-difluorobromobenzene,2,4-difluorobromobenzene, 2,5-difluorobromobenzene,2,6-difluorobromobenzene, 3,5-difluorobromobenzene, 3,5-difluorobenzene,pentafluorobromobenzene, 2,3,5,6-tetrafluorobromobenzene,1-bromo-2,3,5,6-tetrafluorobenzene 2,3,4-trifluorobromobenzene,2,3,5-trifluorobromobenzene, 2,3,6-trifluorobromobenzene,2,4,5-trifluorobromobenzene, 2,4,6-trifluorobromobenzene,3,4,5-trifluorobromobenzene, 2-(trifluoromethyl)bromobenzene,3-(trifluoromethyl)bromobenzene, 4-(trifluoromethyl)bromobenzene,2,4-bis(trifluoromethyl)bromobenzene,2,5-bis(trifluoromethyl)bromobenzene,3,5-bis(trifluoromethyl)bromobenzene,2-fluoro-3-(trifluoromethyl)bromobenzene,2-fluoro-4-(trifluoromethyl)bromobenzene,2-fluoro-5-(trifluoromethyl)bromobenzene,2-fluoro-6-(trifluoromethyl)bromobenzene,3-fluoro-5-(trifluoromethyl)bromobenzene,4-fluoro-2-(trifluoromethyl)bromobenzene,4-fluoro-3-(trifluoromethyl)bromobenzene,2-methyl-3-(trifluoromethyl)bromobenzene,2-methyl-5-(trifluoromethyl)bromobenzene and4-methyl-3-(trifluoromethyl)bromobenzene.

Most preferred tracer compounds have a boiling point greater than 100°C., especially greater than 140° C. at normal atmospheric pressure. Ahigher boiling compound is more difficult to remove by evaporationtechniques including aeration by stirring or sparging air through themarked fuel. Preferably the tracer compound has a boiling point withinthe distillation range of the hydrocarbon liquid or within 10° C. of theboiling point of the hydrocarbon liquid. Preferably the tracer compoundhas a boiling point which is within the distillation range of thehydrocarbon liquid to be marked. More preferably, the tracer compoundhas a boiling point which is within the central 90% of the distillationrange of the hydrocarbon liquid to be marked. Diesel has a boiling rangefrom 180-390° C. Gasoline has a boiling range from 25-215° C. When ahydrocarbon liquid which has a boiling range, such as diesel orgasoline, is to be marked, then a tracer compound having a suitableboiling point would be selected based upon the boiling range of thehydrocarbon liquid. When a hydrocarbon solvent or a liquid having adistinct boiling point, such as hexane, is to be marked then the tracercompound is preferably selected to fall within 10 degrees of the boilingpoint of that hydrocarbon. The tracer compound is a liquid at roomtemperature or it is a solid which is soluble in the quantities at whichit is to be used either in the liquid or in a master-batch formulation.

The tracer compound is added to the hydrocarbon liquid in such an amountas to provide a concentration of the tracer compound which is detectableby readily available laboratory methods capable of identifying thetracer compound in the liquid at the concentrations used. Suitablemethods include, but are not limited to, gas chromatography coupled witha suitable detector such as an electron capture detector or a massspectrometer. The hydrocarbon liquid may be identified as a hydrocarbonliquid containing the tracer by comparing the spectrum or other form ofanalytical result obtained from analyzing the sample with a spectrum orresult obtained from analyzing a standard sample of a known hydrocarbonliquid containing a known concentration of the tracer. The sample resultor a characteristic feature of the result, such as a peak area, may becompared with a value for a corresponding result or characteristic of astandard sample which is held in a memory of a data processing device.Alternatively the result from the sample may be interpreted withoutreferring to a known standard result or sample.

Typically, the concentration of tracer in the hydrocarbon liquid iswithin the range from 1 ppbv (part per billion by volume) to 100 ppbv,the actual amount used depending on the detection method and limit ofdetection of the particular tracer compound used. The tracer compoundmay be present at a higher concentration than 100 ppbv, for example upto 500 ppbv or even up to 1 ppmv (part per million by volume), althoughwhen the product to be marked is a high-volume commodity such as amotor-fuel, economic considerations usually favour lower levels oftracer compound. The tracer compound may be supplied in the form of aconcentrated dosing solution (or master-batch) of the tracer compound ina solvent. In this case the preferred solvent is a liquid which issimilar to the liquid to be marked, although a different solvent, e.g. ahexane or mixed paraffins solvent may be used provided the presence ofsuch a solvent can be tolerated in the hydrocarbon liquid to be marked.The concentrated dosing solution can be added to the hydrocarbon liquidto be marked so as to produce the required final concentration of thetracer compound by dilution. More than one tracer compound may be addedto the liquid.

The selected tracer compound(s) is resistant to laundering by adsorptionon activated charcoal or clay. In a preferred embodiment, at least 50%(more preferably at least 60%, especially at least 80%) of the tracercompound is retained in the hydrocarbon liquid after a sample of theliquid containing the tracer compound has passed through a column offresh activated charcoal. The test to be applied for resistance tolaundering by adsorption on a solid adsorbent is described below.Preferably at least 50% (more preferably at least 60%, especially atleast 80%) of the tracer compound is retained in the hydrocarbon liquidafter a sample of the liquid containing the tracer compound has passedthrough a column of fresh sepiolite clay.

Preferably the selected tracer compound(s) is resistant to laundering bychemical treatment with an acid or a base. In preferred embodiments, atleast 50% (more preferably at least 75%) of the tracer compound isretained in the hydrocarbon liquid after a sample of the liquidcontaining 10-15 ppbv of the tracer compound has been vigorouslyagitated in contact with 10% aqueous HCl. Preferably at least 50% (morepreferably at least 75%) of the tracer compound is retained in thehydrocarbon liquid after a sample of the liquid containing 10-15 ppbv ofthe tracer compound has been vigorously agitated in contact with 10%aqueous H₂SO₄. Preferably at least 50% (more preferably at least 75%) ofthe tracer compound is retained in the hydrocarbon liquid after a sampleof the liquid containing 10-15 ppbv of the tracer compound has beenvigorously agitated in contact with 10% aqueous NaOH. Preferably atleast 50% (more preferably at least 75%) of the tracer compound isretained in the hydrocarbon liquid after a sample of the liquidcontaining 10-15 ppbv of the tracer compound has been vigorouslyagitated in contact with methanolic KOH (3M aqueous KOH diluted 1:10 inmethanol). The test procedure for resistance to laundering by thesechemical treatments is described below.

The invention will be further described in the following examples. Inthe Examples, the test methods which are used are described below. Themeaning of ppb v/v is parts per billion based on the volume of liquidtracer compound in the total volume of liquid. In the following tests,T1 is pentafluorobromobenzene; T2 is 3-(trifluoromethyl)bromobenzene.

Test for Resistance to Removal by a Solid Adsorbant (Charcoal, Clay orSilica Gel)

A 30 cm long chromatography column, having an inside diameter of 1 cm,was filled with the solid adsorbent to a depth of about 15 cm. Theadsorbent was supported in the column on a glass frit. 15 ml of a dieselfuel containing 10 ppb v/v of the test tracer compound was added to thecolumn and allowed to percolate through the adsorbent bed under gravity.The liquid eluting from the column was collected, sealed into anautosampler vial and analyzed immediately by gas chromatography-massspectrometry (GCMS). The amount of tracer detected in the collectedliquid is reported below in Table 1, as a percentage of the originalconcentration. Approximately 5 ml of liquid was retained on the column,presumably in the pores and voidage of the adsorbent particle bed.

The adsorbents used were:

-   Charcoal:—a powdered activated Norit™ charcoal (type RBAA-3) from    Fluka (product number 29238),-   Sepiolitic clay: a pure fine sepiolite clay from RS Minerals-   Silica gel 60 from Fluka (product number 60738)-   Fine powdered Al₂O₃ from Sigma Aldrich (product number 11028)-   Aluminium hydroxide, fine powder from Sigma Aldrich (product number    23918-6)-   Kaolin: fine powder from Sigma Aldrich (product number K7375)

TABLE 1 Adsorbent Tracer Sepiolitic compound clay Charcoal Silica gelAl₂O₃ Al(OH)₃ Kaolin T1 90 88 94 97 91 100 T2 99 87 92 95 93 98

Multi-Pass Adsorbant Test

The above test procedure was carried out using 50 ml of diesel fuelmarked with 10 ppb v/v of the tracer compound and the eluted liquid wascollected in an open beaker before being passed through a second columnpacked with fresh adsorbent. The liquid from the second column wascollected in an open beaker before being passed through a third columnpacked with fresh adsorbent. A sample of the liquid collected from eachcolumn was taken for analysis by GCMS and the concentration of thetracer in the eluted liquid is shown in Table 2 as a percentage of theoriginal concentration. When the concentration is greater than 100%, itis believed that the diesel fuel was retained on the adsorbent inpreference to the tracer so that the solution became more concentrated.

TABLE 2 Tracer Sepiolitic clay Charcoal compound 1^(st) pass 2^(nd) pass3^(rd) pass 1^(st) pass 2^(nd) pass 3^(rd) pass T1 93 73 53 78 68 41 T2102 99 94 70 40 18

Test for Loss of Tracer Compound on Standing

1 ml of diesel fuel marked with 10 ppb v/v of the test tracer compoundwas placed in an open topped 2 ml autosampler vial, and repeatedlyanalyzed by GCMS over the course of one day after standing in normallaboratory conditions to determine the concentration of the tracercompound in the diesel. The samples were interspersed with sealedcalibration standards to correct for any instrument drift over theperiod of analysis. The concentration of the tracer in the liquid isshown in Table 3 as a percentage of the original concentration. When theconcentration is greater than 100%, it is believed that the diesel fuelevaporated more quickly than the tracer so that the solution became moreconcentrated.

TABLE 3 T1 T2 Concentration of tracer after 24 hours (%) 97 95

Test for Stability to Ultra-Violet Radiation

20 mls of diesel fuel marked with 10 ppb v/v of the test tracer compoundwere placed in each of two headspace vials which were sealed withairtight crimp tops, one of which was exposed to 365 nm UV light, theother left shaded on the laboratory bench. After 24 hours, approximately0.5 mls was removed from each vial for analysis and crimp caps replacedwith new. This was repeated again after 52 hours. Table 4 shows the % ofthe original concentration of tracer found by GCMS in the treated sampleat the time shown.

TABLE 4 Tracer compound 0 hrs 24 hrs 52 hrs T1 100 94.6 87 T2 100 9891.2

Test for Resistance to Removal by Chemical Treatment

A quantity of the diesel fuel marked with 13 ppb v/v of the test tracercompound was shaken vigorously with an equal volume of a chemical agentselected from 10% HCl in deionised water, 10% H₂SO₄ in deionised water,10% NaOH in deionised water and methanolic KOH (3M aqueous KOH diluted1:10 in methanol). The mixture was allowed to settle, then shaken for afurther minute before settling again. A sample of the diesel layer wasanalyzed by GCMS and the concentration of the tracer in the treateddiesel liquid is shown in Table 5.

TABLE 5 Tracer 10% 10% 10% compound HCl H₂SO₄ NaOH KOH/MeOH T1 78 87 8685 T2 73 89 88 88

What is claimed:
 1. A method of identifying a hydrocarbon liquidcomprising the steps of: adding to said liquid,1,3-dibromotetrafluorobenzene as a tracer compound, and subsequentlyanalyzing a sample of a hydrocarbon liquid for the presence of saidtracer compound to determine whether said sample is a sample of saidmarked hydrocarbon liquid.
 2. The method according to claim 1, whereinat least 50% of the tracer compound is retained in the hydrocarbonliquid after a sample of the liquid containing from 10 to 15 ppbv of thetracer compound has passed through a column of fresh activated charcoal.3. The method according to claim 1 , wherein at least 50% of the tracercompound is retained in the hydrocarbon liquid after a sample of theliquid containing from 10 to 15 ppbv of the tracer compound has passedthrough a column of fresh powdered sepiolitic clay.
 4. The methodaccording to claim 1, wherein the tracer compound has a boiling pointwithin the distillation range of the hydrocarbon liquid or within 10° C.of the boiling point of the hydrocarbon liquid.
 5. The method accordingto claim 1, wherein more than one tracer compound is added to thehydrocarbon liquid.
 6. The method according to claim 1, wherein thetracer compound is added to the hydrocarbon liquid in such a quantity asto produce a final concentration in the liquid of from 1 to 500 ppbv. 7.The method according to claim 6, wherein the tracer compound is added tothe hydrocarbon liquid in such a quantity as to produce a finalconcentration in the liquid in the range from 1-100 ppbv.
 8. The methodaccording to claim 1, wherein at least 50% of the tracer compound isretained in the hydrocarbon liquid after a sample of the liquidcontaining from 10 to 15 ppbv of the tracer compound has been vigorouslyagitated in contact with 10% aqueous HCl.
 9. The method according toclaim 1, wherein at least 50% of the tracer compound is retained in thehydrocarbon liquid after a sample of the liquid containing from 10 to 15ppbv of the tracer compound has been vigorously agitated in contact with10% aqueous H₂SO₄.
 10. The method according to claim 1, wherein at least50% of the tracer compound is retained in the hydrocarbon liquid after asample of the liquid containing from 10 to 15 ppbv of the tracercompound has been vigorously agitated in contact with 10% aqueous NaOH.11. The method according to claim 1 , wherein at least 50% of the tracercompound is retained in the hydrocarbon liquid after a sample of theliquid containing from 10 to 15 ppbv of the tracer compound has beenvigorously agitated in contact with methanolic KOH.
 12. A hydrocarbonliquid containing a tracer compound as used in claim 1 at aconcentration of from 1 to 500 ppbv.